Automatic steering system



June 16, 1953 A. M. M CALLUM 2,642,554

AUTOMATIC STEERING SYSTEM Filed Jan. 25, 1947 3 Sheets-Sheet 1 SERVO AMPfig/l AMPLIFIER INVENTOR TORNEY June 16, 1953 A. M. M cALLuM AUTOMATICSTEERING SYSTEM 3 Sheets-Sheet 2 Filed Ja n. 25, 1947 INVENTOR AT ORNEYJune 16, 1953 A. M. M CALLUM AUTOMATIC STEERING SYSTEM 3 Sheets-Sheet 5Filed Jan. 25, 1947 INVENTOR flLfi/V M. MHL EHLLUM TTORNEY Patented June16, 1953 UNITED STATES. PATENT OFFICE 7 5342554 an 7 v AUTQMATTIQNGSWTEMT j Alan'M; MacCallum, *Maywood, N. J assignor to Bendix-AviationCorporation, .Teterbo'ro, N. J a corporation of-Delaware..; tApplication January23, 1947, Serial N6. 723,829

13,. c *Thepresent inventionrelates toa-n-'electric-' automatic pilotadapted 'foruse -with dirigi-ble craftand one which may be" appliedequally as well to the automatic steering of bothair and water craft. ai

r In an electric automaticpilot variousmethods are employed whereby thedisplacement signal for, each axis of control is derived from a relatedelectrical instrument and transmittedto operate an electric servomotorof the related control surface so. that-a; rapid response on the part ofall the necessary control surfaces is obtained. -One of the methods inthe creation and-transmission of displacement signals utilizes theinherent 'characteristics of inductivedevices in conjunction with anelectronic gdirection, discriminating device as more fully described in"pending application SeriaLNo. 516,488, filed December 31 1943. While the7616013171? automatic pilot described in the above-mentioned pendingapplication performs in a manner superior to any other prior device,commercial operation has disclosed certain latent defects "which areovercome by means" of the novel arrangement of the present invention.For example, it is possible that upon the occurrence of certainconditions, the automatic pilot of the abovecopending application may besubjected to a hard-over signal of sufiicient magnitude to throw thecraft out of control. Moreover, asf'a result of the arrangement ofsignal devices and amplification channels there utilized, onesided'control and/or false operation may be obtained; An object of the presentinvention, therefore, is t'o provide. a novel; and improved automaticsteeringsystem for m obile'craft. r Ano e obj t. oft e pr sg tg n l fiil M9, provide novel safety features in an automatic pilot which willincrease the safety fact o r-in the flying of aircraft. J 7

Ir furtherobject' is to provide novel improvements in automaticsteeringsystems which will remove latent sources of danger heretofore existilijgth r A still further object is to provide a novel safety featurewhereby, the possibility of creating a hard over control signal has beeneliminated from an automatic pilot.

Another object is to provide novel means by the occurrence of one sidedcontrol is eliminated from the" operation of an automatic pilot.

A' further object of the present invention .is to provide novel meanswhereby the. occurrence of falsejoperations in the functioning of anauto'- matic pilot is reduced to a minimum.

"The foregoing 'and'other' objects and advan 4 Claims. (Cl. 318-28)wheretages- 'of the--invention"will appear more i fully hereinafter fromconsideration of the detailed description which follows, taken togetherwith the accompanyingdrawi ngs wherein one embodiment of-theinventionisillustrated by way ofaexamplei It isto be expresslyunderstood, howevergthat the drawings are for illustrative purposesonly, andare not to be construed as defining the limits of theinvention, reference being had for this-purpose to the appended claims;

In thedrawings, wherein'like reference numerals refer to like parts: '11 1 Figure 1 is a schematic diagram and representation of the rudderchannel of the automatic pilot.

Figure 2 is a schematic diagram and representation of the elevator andaileron channels of the automatic pilot..

Figure 3 is a schematic diagram of the electronic directiondiscriminationdevice and amplifier. r v p V For abetter understanding ofthe present invention, reference is made to thecopending applicationreferred to above wher in the theory and operation of the electric pilothereof is fully set forth. As there shown, inductive transmittingdevices, comprising three phase wound stators inductively associatedwith wouncl rotors connected to thecrafts, sourcerof, alternatingcurrent potential, areprovided, and connected to reference meansresponsive to axial deviations of the craft from neutral axes forgenerating electrical displacement signals resulting fromsuchdeviations. In response to the deviations, potentials are generatedinthestator windings of each transmitter proportional, jrespectively,to theangular position of each stator winding preach transmitter with p t.tQ-..the e a ed .-r 2 wi v a d are transmitted tqthree, phase woundstators of inu 't y recei r. dev c s. bar n Wound r to ucti rgias biateclt r w t For. a dis: p eg entc ndii n c r raf bouie y of it aizes,a condition of electrical equilibrium' exists eiw enrt iet ans ter an rce er whereby fi qfili .2 1 335. 91 t r e er rotors are malto theresultantmagnetic fields of the receiver stators. so thatnopotentialsare induced Within the yarious receiver rotor windings, Assoon, howevenas an angular displacement of the craft occurs about itsvarious axes the'transmitter rotors are angularly displaced relative totheir related stators: generating new values of potential intheilatterwhereby the condition oi equilibrium previouslyeiristingbetween thetransmitters and ersis destroyed,. l n'this manner thedirec-" iron resultant-magnetic fields ofthe re= ceiver stators arechanged so that they are no longer normal with the electrical axes ofthe receiver rotors whereby potentials are induced in the latter whosemagnitudes are proportional to the amount of angular deviations from thevarious neutral axes.

Deviations of the craft from the neutral axes in one direction inducesin the receiver rotors potentials whose magnitudes are proportional tothe amount of deviation and having definite phases or polarities withrespect to the crafts source of alternating current potential.Deviations of the craft from the neutral axes in the opposite directioninduces in the receiver rotors potentials whose magnitudes areproportional to the amount of deviations but having phases or of a rateof turn gyroscope 20 while device I2 polarities 180 out of phase withthose induced during deviations in the first direction.

The phase shift in the potentials of the re-' 1 nitudes of potentialsinduced in the receiver rotors. The direction of deviation determineswhether the potentials of the receiver rotors are in phase or 180 out ofphase with the crafts source of alternating current potential. Signalpotentials are thus created whereby the direction of deviationsdetermines the phase shift and the amounts of deviation determine themagnitude of the potentials.

The axial displacement signals created by a change of the craftsattitude are amplified in order to operate the servomotors of therelated control surfaces. These signals are impressed upon the grid ofan amplifier tube of either the rudder, aileron or elevator channels,the plate of which connects through a pair of parallel leads with thegrids of two phase discriminating tubes, the anodes of the latterbeingconnected to opposite terminals of a grounded split secondary winding ofa potential transformer thus making the plate potentials of thediscriminator tubes 180 out of phase with each other. Saturabletransformers connect with theplate circuits of the discriminator tubesandwith the related servomotors so that the latter are energized inresponse to displacement signals, the direction of operation dependingupon the phase of the incoming displacement signals which, in turn,determine the conductivity of one or the other of the discriminatortubes.

One disadvantage encountered with the use of the above discussedinterdependent signal sources has been that in the event of an' open orshort circuit in the connection of the three phase stators of thetransmitting and receiving devices, sudden unbalanced potentials areinduced in the receiver rotors creating hard-over. signals.

which are applied to the related control surfaces causing the craft tobe thrown out of con- I trol.

To the end that the foregoing disadvantage may be overcome, the novelarrangement constituting the subject matter of the present invention isprovided with the use of which interdependent signal sources have beeneliminated. For this purpose single phase variable inductive devicescomprising single phase wound stators associated with single phase woundrotors have been provided. As shown in Figure 1 of the drawings, threesuch devices IIl, II and I2 are utilized in the rudder channel.Device-I0 comprises a single phase statorI3 and a single phase comprisesa single phase stator 2| and an inductively coupled single phase rotor22 connected ,to a-shaft23 which is driven through a gear system 24 by'arudder servo 25. Angular displacemerit of any one or all of shafts I5,I9 and 23 displaces the magnetic fields of rotors I4, I8 and 22, whichare connected through suitable resistors 26 with the crafts source ofalternating current (not shown), from a normally electrically balancedcondition relative to stators -I3,

I! and 2I so that signal potentials are induced therein. The potentialsof the various stators are impressed across the fixed terminals ofresistors 21, 28 and 29, the latter tWo being variable for a purpose topresently appear and engaged by slidable contacts 30 and 3|, and fed inseries to the input of the rudder channe1 amplifiers 32 whose output isconnected by way of leads 33 with motor 25. 1

Where the deviation of the craft from a neutral axis necessitates thecorrective action of more than one element of control such as the.rudder channel, for example, the signal voltage with each other. Thisbecomes apparent in view of the fact that were not the individual signalpotentials in phase they couldbe added only vectorially whereby a signalpotential would be derived which would not be a function of all the Thisobject is attained by. connecting the resistors 26 in series with theelements of control.

windings of rotors I4, I8 and 22 to maintain the signal voltages inphase, and by arranging resistors 21, 28 and 29 acros'sthe statorwindings ,to maintain the amplitudes of the signal voltagessubstantially equal for equal displacements of their related rotorwindings, in which event' the phases of the signal potentials of eachelement of control can be initially adjusted so that all will bemaintained in phase with each other and their amplitudes for equaldisplacement of their related rotors maintained substantially equal.

As in the case of the rudder channel, the three phase wound inductivedevices have been eliminated from the aileron and elevator controlchannels and in their stead, in accordance with the present invention,single phase variable inductive devices have been provided. As shown in.Figure 2 of the drawings, an inductive bank device 34 is providedhaving a single phase stator 35 and a single phase rotor 36 connected toa trunnion 31 of a gyro vertical 38. For elevator control, a secondsingle phasev variable inductive device is provided havinga single phasestator 39 anda single phase rotor 40 connected to a trunnion 4| of thegyro vertical.

Bank device 34 is connected in series with the input of the aileronchannel of an amplifier .88 and with a single phase wound stator 43 of afollow-up device 44 having associated therewith an angularly movablesingle phase rotor 45, the latter being displaceable through a reductiongear system 46 by a servomotor 41 which is connected to the output ofthe amplifier aileron channel by way of leads 48. a a i Stator 39 of thepitch device 42 is connected in series with the input of the elevatorchannel of amplifier 88 and with a single phase wound stator 49 of afollow-up device '50 having associated therewith an -angularly' movablesingle phaserotor 5| which is displaceable through a reduction gearsystem 52-by way of a servomotor 63,- the latter being connected totheoutput of the amplifier elevator channel by way of leads 54. Stators 43and 49 ofthe follow-up devices 44 and 50 have resistors 55.v and 56arranged across their terminals which are 'engage'dby adjustablecontacts- 51 and-58 while.rotors 45 and 5| connect with the craft?ssource of alternating current- (not shown) l through resistors 59and-$9. I I 1 In the foregoing manner, the use of interdependent signaldevices inthe rudder, aileron and elevator'ch annels of sameness pilotand their surrounding disadvantages have been eliminated. With the novelarrangement of single phase variable inductive devicesconnectedin-series no signal will be communicated'to the grids oftheamplifier channels in the event of a break in their connection asdistinguished from the hardover signals previously developed by a breakin the connections of interdependent signal sources.

While the novel arrangement set forth above has eliminated thepossibility of hard-over control signals, a break in the connectinglines to grids 6!, 62 and 63 of amplifier tubes 64, 65 and 66 of therudder, aileron and elevator channels, shown in Figure 3, will result inpicking up stray potentials and communicating them to the grids whichare provided with a normally negative bias. Such stray potentials arenormally greater than the negative grid bias butsmaller than the signalpotential developed by the inductive devices whereby operation of theamplifier will occur in response to the stray potentials resulting infalse operation of the related control surfaces. To the end that falseoperation due to stray potentials may be overcome, a negative cut-offbias is impressed upon the grids BI, 62 and 63 from the negative sidesof batteries 610., 68a and 69a through resistors 61, 68 and 69, suchbias being of a magnitude greater than any stray potential that may bedeveloped because the resistance value of each of the resistors 61, 68and 69 is greater than the respective input impedances to the vacuumtubes 64, 65 and 66.

By the novel provision of the negative cut-01f bias on the grids throughresistors 61, 68 and 69 the amplifier channels are rendered inoperativeand unresponsive to all voltages applied to grids 6|, 62 and 63 having amagnitude less than the applied negative bias but will operate inresponse to signal voltages, The normal low impedance input circuits actas short circuits on the cut-off bias supplied through resistors 61, 68and 69. In this manner novel provision is made in the input circuits ofthe amplifier channels so that in the event open circuits occur, anegative cut-off bias is automatically applied to the input tubescausing the channels affected to go dead rather than subjecting therelated control surfaces to the effect of stray pick-up voltages.

A further disadvantage resulting with the use oftlieauto'm'atic pilot ofthe above referred'to copending application resided'in'the possibilityof one sided control in any one or more of the control channels oftheamplifier due to the fact that the heater circuits of thediscriminator tubes of each channel were connected in parallel. Thus,theburning out of one heater element of one discriminator tube of onechannel resulted in blocked operation for one side of that controlchannel whereby response was available for only one direction ofdeviation from a neutral axis. To the endthat the occurrence ofone-sided control in any one or more control channels may beleliminated,heater elements 10, H of discriminator tubes 72,13 of the amplifierrudder channel aswellas heater elements 14, 15 of tubes 16,-" of theamplifier aileron channel and heater elements l8, T9 of tubes 86, 8! ofthe amplifier elevator channel are connected in series with suitablecurrent sources such as batteries 82, 83 and 84,---for examplerby. wayof leads 85, 86 and 81 as shown in Figure With this novel arrangement;if any one 'of the heater elements of any one or more control channelsburns out, the whole channel automatically becomes inoperative therebypreventing one sided control in any one or more of the control channels.

--Although but one embodiment of the invention has been illustrated anddescribed, various changes and modifications in the form and relativearrangement of parts, which will now appear to those skilled in the art,may be made without departing from the scope of the invention. Referenceis therefore to be had to the appended claims for a definition of thelimits of the invention.

I claim:

1. In an automatic pilot for aircraft having a I movable control surfacethereon and a servomotor for operating said surface, reference meansincluding a variable inductive device having a single phase wound statorand an inductively coupled angularly movable single phase wound rotorfor developing in said stator a signal in response to a departure bysaid craft from a predetermined position for operating said motor, rateof departure means comprising a rate-of-turn gyroscope and a secondvariable inductive device controlled thereby and having a single phasewound stator and an inductively coupled angularly movable single phasewound rotor for developing in said second-named stator a signal inresponse to the rate of departure by said craft from said predeterminedposition for modifying the operation of said motor, a third variableinductive device comprising a single phase wound stator and aninductively coupled angularly movable single phase wound rotorresponsive to the operation of said motor for developing in saidlast-named stator a follow-up signal for further modifying the operationof said motor, means connectin said rotors for energization from asource of alternating current, means connecting said stators in serieswith one another for controlling operation of said motor, meansconnected to the rotors of at least two of said variable inductivedevices for controlling the phase of the signal developed therein withinan angle of less than 18 0 degrees, and means connected to the stator ofat least two of said variable inductive devices for controlling the manitude of the signal developed therein independently of the phase of thesignal.

2. In a device of the kind described wherein a signal is developed inresponse to a change in condition, thermionic means having an input ofrelatively low impedance adapted to receive the signal, a relativelyhigh impedance connected to said input, and biasing-means cooperatingwith said relatively high impedance and providing for the passage ofsignals to said thermionic means during normal operation and biasingsaid thermionic means to cutofi, in the event of anopen circuit in saidinput, and rendering said thermionic means inoperative to stray signals.

o 3. The combination with an automatic pilot for an aircraft having amovable control surface thereon anda servomotor for operating saidsurface together with reference means for developing a signal inresponse to a departure by said craft from a predetermined position foroperating said motor, of thermionic means interconnecting said motorwith said reference means and having an input of relatively lowimpedance adapted to receive the signal, a relatively high impedanceconnected to said input, and biasing means connected to said relativelyhigh impedance to bias said thermionic means to cutoff in the event ofan open circuit in said input.

4. The combination with an automatic pilot for an aircraft having amovable control surface thereon and a servomotor for operating saidsurface, together with reference means including a variable inductivedevice having a single phase stator Winding and an inductively coupledangularly movable single phase rotor winding for developing in one ofsaid windings a signal, in response to a departure by said craft from apre- References Cited in the file of this patent UNITED STATES PATENTSNumber Name Date 1,942,587 Whitman .Jan. 9, 1934 2,014,825 Watson Sept.17, 1935 2,115,086 Riggs Apr. 2-6, 1938 2,209,369 Wills July 30, 19402,336,492 MacKay Dec. 14, 1943 2,416,097 Hansen et al. Feb. 18, 19472,429,642 Newton Oct. 28, 1947 Young Mar. 15, 1949

